Intrinsic and acquired resistance to HER-targeting drugs occurs in a significant proportion of HER2-overexpressing breast cancers. Thus, there remains a need to identify predictive biomarkers that could improve patient selection and circumvent these types of drug resistance. Here, we report the identification of neuromedin U (NmU) as an extracellular biomarker in cells resistant to HER-targeted drugs. NmU overexpression occurred in cells with acquired or innate resistance to lapatinib, trastuzumab, neratinib, and afatinib, all of which displayed a similar trend upon short-term exposure, suggesting NmU induction may be an early response. An analysis of 3,489 cases of breast cancer showed NmU to be associated with poor patient outcome, particularly those with HER2-overexpressing tumors independent of established prognostic indicators. Ectopic overexpression of NmU in drug-sensitive cells conferred resistance to all HER-targeting drugs, whereas RNAi-mediated attenuation sensitized cells exhibiting acquired or innate drug resistance. Mechanistic investigations suggested that NmU acted through HSP27 as partner protein to stabilize HER2 protein levels. We also obtained evidence of functional NmU receptors on HER2-overexpressing cells, with the addition of exogenous NmU eliciting an elevation in HER2 and EGFR expression along with drug resistance. Finally, we found that NmU seemed to function in cell motility, invasion, and anoikis resistance. In vivo studies revealed that NmU attenuation impaired tumor growth and metastasis. Taken together, our results defined NmU as a candidate drug response biomarker for HER2-overexpressing cancers and as a candidate therapeutic target to limit metastatic progression and improve the efficacy of HER-targeted drugs. Cancer Res; 74(14); 1–13. ©2014 AACR.

Although specific mutations in the tyrosine kinase domain of epidermal growth factor receptor (EGFR) identify tumors that are responsive to EGFR tyrosine kinase inhibitors (TKI), these genetic alterations are present in only a minority of patients. Patients with tumors expressing wild-type EGFR lack reliable predictive markers of their clinical response to EGFR TKIs. Although epithelial–mesenchymal transition (EMT) has been inversely correlated with the response of cancers to EGFR-targeted therapy, the precise molecular mechanisms underlying this association have not been defined and no specific EMT-associated biomarker of clinical benefit has been identified. Here, we show that during transforming growth factor β (TGFβ)–mediated EMT, inhibition of the microRNAs 200 (miR200) family results in upregulated expression of the mitogen-inducible gene 6 (MIG6), a negative regulator of EGFR. The MIG6-mediated reduction of EGFR occurs concomitantly with a TGFβ-induced EMT-associated kinase switch of tumor cells to an AKT-activated EGFR-independent state. In a panel of 25 cancer cell lines of different tissue origins, we find that the ratio of the expression levels of MIG6 and miR200c is highly correlated with EMT and resistance to erlotinib. Analyses of primary tumor xenografts of patient-derived lung and pancreatic cancers carrying wild-type EGFR showed that the tumor MIG6(mRNA)/miR200 ratio was inversely correlated with response to erlotinib in vivo. Our data demonstrate that the TGFβ–miR200–MIG6 network orchestrates the EMT-associated kinase switch that induces resistance to EGFR inhibitors, and identify a low ratio of MIG6 to miR200 as a promising predictive biomarker of the response of tumors to EGFR TKIs. Cancer Res; 74(14); 1–11. ©2014 AACR.

New therapeutic targets are needed that circumvent inherent therapeutic resistance of glioblastoma multiforme (GBM). Here, we report such a candidate target in the uncharacterized adaptor protein hMOB3, which we show is upregulated in GBM. In a search for its biochemical function, we found that hMOB3 specifically interacts with MST1 kinase in response to apoptotic stimuli and cell–cell contact. Moreover, hMOB3 negatively regulated apoptotic signaling by MST1 in GBM cells by inhibiting the MST1 cleavage-based activation process. Physical interaction between hMOB3 and MST1 was essential for this process. In vivo investigations established that hMOB3 sustains GBM cell growth at high cell density and promotes tumorigenesis. Our results suggest hMOB3 as a candidate therapeutic target for the treatment of malignant gliomas. Cancer Res; 74(14); 1–11. ©2014 AACR.

Adenosine targeting is an attractive new approach to cancer treatment, but no clinical study has yet examined adenosine inhibition in oncology despite the safe clinical profile of adenosine A2A receptor inhibitors (A2ARi) in Parkinson disease. Metastasis is the main cause of cancer-related deaths worldwide, and therefore we have studied experimental and spontaneous mouse models of melanoma and breast cancer metastasis to demonstrate the efficacy and mechanism of a combination of A2ARi in combination with anti-PD-1 monoclonal antibody (mAb). This combination significantly reduces metastatic burden and prolongs the life of mice compared with either monotherapy alone. Importantly, the combination was only effective when the tumor expressed high levels of CD73, suggesting a tumor biomarker that at a minimum could be used to stratify patients that might receive this combination. The mechanism of the combination therapy was critically dependent on NK cells and IFNγ, and to a lesser extent, CD8+ T cells and the effector molecule, perforin. Overall, these results provide a strong rationale to use A2ARi with anti-PD-1 mAb for the treatment of minimal residual and metastatic disease. Cancer Res; 74(14); 1–7. ©2014 AACR.